Metals in powder form are used to produce many useful articles. For example, fine metal powders can be pressed and sintered into shapes such as gears and the like for use in machinery. Parts produced by means of powder metallurgy can be made to precise tolerances with minimum amounts of finishing operations and from metals that may otherwise be difficult to fabricate.
The key to producing metal powders by gas atomization is the gas atomization nozzle. The nozzle must be such that it will provide uninterrupted atomization of the molten metal stream. A high pressure gas stream passing through the gas atomization nozzle impinges upon a molten metal stream breaking up and quenching the molten stream to form metal powder. Gas pressure and flowrate are critical to the process since the metal powder particle size is directly related to the gas pressure and the flowrate is directly related to the ability of the molten metal to be adequately quenched. Present nozzle technology relies upon control of the flowrate by means of the size of the nozzle orifice. The orifice size is typically fixed or manually set prior to the production of the metal powder. Since the nozzle orifice is manually set if the size is not controlled properly excessive gas usage will result in freezing of the metal stream which halts production. Prior art devices have sought better flow control in order to provide consistent uninterrupted production and allow optimization of gas flowrate for the desired alloy and powder characteristics. In addition optimization of the flowrate would reduce gas flowrates which provides an economic benefit to the user.
U.S. Pat. No. 4,416,600 discloses and claims a nozzle which is made of several pieces wherein the nozzle insert uses a spiral channel in order to effect control of the gas flow and the resultant size of the particles produced.
U.S. Pat. No. 3,253,783 discloses and claims a gas atomization nozzle wherein the gs is introduced into a plenum chamber through tangantial slots from an annular chamber and then from the plenum chamber to passages outwardly of the nozzle around the molten metal stream to effect production of the powder.
U.S. Pat. No. 4,619,597 discloses and claims a gas atomization nozzle with specific relationship between the outer surface of the melt tube and the plenum closure plate orifice.
U.S. Pat. Nos. 1,856,679, 3,501,802, 2,440,531, 3,592,391, and 3,901,492 all disclose and claim gas atomization nozzles which have attempted to provide a control of the particle size and the gas flow.
However, with all of these prior art devices flow control has been limited to manual inspection and machine tolerance specifications between the metal tube and the surrounding orifice in order to determine the nozzle opening. Since most nozzle devices are subjected to extremely high temperatures caused by the molten metal the assembly warps and thus the orifice (annulus) changes in size and uniformity.